This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on German Patent Application No. 102 37 608.5 filed in Germany on Aug. 16, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a camera arrangement for motor vehicles, with a camera that is arranged behind a window (windshield).
2. Description of the Background Art
A camera arrangement is taught in DE 40 16 570 A1, for example. However, a problem in camera arrangements of this nature is fogging on the inside surface of the window, which is caused by condensation of water vapor on the relatively cold glass in the vehicle interior, especially in winter. A fogged interior window surface seriously impairs image acquisition by the camera, or even makes it impossible.
It is therefore an object of the present invention to provide a camera arrangement such that fogging on the interior surface of the window is prevented in the camera""s field of view.
The idea upon which the invention is based to attain this object is in arranging a transparent additional window behind and a distance away from the windshield, at least in the portion of the windshield viewed by the camera, so that a layer of air is enclosed between the window and the additional window. This layer of air functions as a thermally insulating layer, achieving the result that the temperature of the additional window never differs very strongly from the temperature of the vehicle interior, even when the windshield is very cold. In other words, the temperature of the enclosed layer of air remains substantially the same as the ambient temperature of the vehicle interior. Consequently, condensation from water vapor on the additional window is avoided, since the window does not represent a xe2x80x9ccold trapxe2x80x9d in the vehicle interior. In addition, the volume of air enclosed between the windshield and the additional window is so small that the absolute quantity of water vapor present in this volume is not enough to form fogging that would impair the camera""s view.
Tests in an environmental chamber demonstrated that the fog-inhibiting effect occurs reliably when the distance between the windshield and additional window is less than 3 mm. In particular, the fog-inhibiting effect is especially good at a distance between 1 mm and 2 mm, because a sufficiently thick layer of air is present for thermal insulation on the one hand, and on the other hand the enclosed volume of air and the absolute quantity of moisture thus enclosed is sufficiently small.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.